The present invention relates to a method and to a machine for treating uniting bands which are used in filter tipping or like machines to connect rod-shaped articles end-to-end, especially to connect plain cigarettes with filter mouthpieces so as to form filter cigarettes of unit length or multiple unit length.
A filter tipping machine comprises means for subdividing an adhesive-coated web of uniting band material into discrete uniting bands which are thereupon rolled around the joints or points of abutment between plain cigarettes and aligned filter mouthpieces. In many instances, a group of coaxial rod-shaped articles which are to be joined by uniting bands consists of two spaced-apart plain cigarettes and a filter rod section of double unit length therebetween. A properly applied uniting band surrounds the filter rod section and the adjacent inner end portions of the plain cigarettes, and the resulting filter cigarette of double unit length is thereupon severed midway across the convoluted uniting band to yield two filter cigarettes of unit length.
As a rule, the adhesive which is applied to webs of uniting band material in a filter tipping machine (such webs normally consist of cigarette paper or imitation cork) is an aqueous dispersion of polyvinyl acetate glue. An important advantage of such glue is that it does not bind for a relatively long period of time subsequent to application to the web, and this is desirable in a filter tipping machine wherein the adhesive-coated web of uniting band material must be subdivided into discrete uniting bands, the bands attached to groups of coaxial rod-shaped articles and the groups transported to the wrapping or rolling station where the groups are rotated about their respective axes to thereby convolute the uniting bands therearound. The adhesive is applied by a paster which comprises one or more adhesive-applying rollers. A freshly applied uniting band extends substantially tangentially of the respective group of coaxial articles and is converted into a tube during rolling of the respective group in a gap whose width at most equals the diameter of the filter mouthpieces and/or plain cigarettes. The device which rolls the uniting bands around the respective groups of coaxial articles is heated to ensure rapid expulsion of water and attendant strengthening of the bond between the convoluted uniting band and the adjacent portions of the filter mouthpiece and plain cigarette or cigarettes.
The relatively long "open time" of adhesives which contain water or another evaporable liquid presents problems in connection with the processing of certain types of rod-shaped articles which constitute or form part of smokers' products. For example, aqueous dispersions of polyvinyl acetate glue are not satisfactory adhesives for attachment of uniting bands to unwrapped filter plugs, the so-called NWA filters, or for use in connection with highly porous wrapping materials. The main reason for development of problems in connection with the utilization of aforementioned types of adhesive as a means for attaching uniting bands to NWA filters is that the surfaces of such filters are fibrous and, therefore, an aqueous dispersion of polyvinyl acetate glue cannot establish an acceptable bond between such rough surfaces and the uniting bands. In other words, the force with which a wet adhesive of the just outlined character bonds the uniting band to an NWA filter is too weak to ensure adequate sealing action and/or retention of the uniting band in optimum position during transport toward and during treatment at the rolling or convoluting station of a filter tipping machine. If the uniting band material is overly porous, an aqueous dispersion of glue is likely to penetrate through the pores of uniting bands and to affect the appearance of the ultimate products as well as to bond the neighboring products to each other. Penetration of an aqueous dispersion of glue through a uniting band which consists of highly porous material is promoted by the long "open time" of such adhesives, i.e., by the fact that it takes the adhesive a relatively long time to set.
The aforementioned problems which arise in connection with the utilization of aqueous dispersions of glue can be avoided or solved by resorting to hotmelts. However, the cost of hotmelts is much higher for a number of reasons, especially because a hotmelt must be activated by heating prior to application to a web of uniting band material. Furthermore, and since the distance between the locus of application of adhesive in a filter tipping machine and the rolling or convoluting station is quite substantial, a hotmelt which has been heated in or in the region of the paster (i.e., at the locus of application of such heat-activatable adhesive to one side of a web of cigarette paper, artificial cork or a similar uniting band material) must be heated again prior to rolling of the uniting bands in order to ensure that each and every uniting band will form a tube which airtightly connects a filter plug to one or two plain cigarettes. Furthermore, and in order to guarantee rapid setting of hotmelt upon completion of the rolling operation, it is normally necessary to cool the convoluted uniting bands of freshly formed filter cigarettes. Heating of hotmelt in the region of the rolling or convoluting station as well as cooling of the freshly formed filter cigarettes presents problems in a filter tipping machine for a variety of reasons, not only as regards the space requirements but also in connection with the energy consumption, accessibility to the rolling station, likelihood of charring of the product at the rolling station and others.